The pineal gland is a small, pine cone-shaped endocrine organ located deep within the brain. Despite its obscured position and diminutive size, the pineal gland has wide-ranging roles regulating our sleep, development and even consciousness. Understanding pineal gland anatomy provides insight into this gland’s multitude of functions.
Pineal Gland Location
The pineal gland sits centrally in the middle of the brain, surrounded by the two hemispheres. It is situated behind and above the pituitary gland, near the upper end of the brainstem.
More specifically, it rests in a tiny hollow or recess called the pineal recess. This is located at the back margin of the third cerebral ventricle, above the corpora quadrigemina and behind the stria medullaris.
The pineal is attached to its recess by a stalk known as the pineal peduncle. It extends 5-8mm from its attachment site and is around 6-8mm wide in adults.
External Structure and Shape
The pineal gland gets its name from its resemblance to a pine cone. It is reddish-gray and weighs about 100 to 180 milligrams on average.
The gland is shaped like a pine cone with a defined “stalk” region leading into a “body” with a rough, lobed surface similar to a pine cone. It is generally rounded or oval in shape.
Calcium concretions and calcified secretion granules often develop on the pineal gland surface as it ages. These contribute to its pine cone-like appearance.
Internal Anatomy
Despite its small proportions, the pineal gland has a complex interior structure:
Parenchymal Cells
Parenchymal cells make up the pineal glandular tissue. They produce and secrete hormones like melatonin and other molecules. Two main parenchymal cell types exist:
- Pinealocytes – The most abundant cell in the pineal at around 70-80%. Pinealocytes synthesize and release melatonin.
- Interstitial cells – Make up 15-20% of pineal cells. Their function is less understood but they interact with pinealocytes.
Glial Cells
Glial cells provide support, nutrients and protective tissue coverings. The pineal gland contains specialized astroglial cells with distinct properties suited to pineal function and interaction with pinealocytes.
Cell matrix
This makes up the supportive tissue between parenchymal and glial cells. It contains blood vessels, nerve fibers, connective tissue, fibroblasts and extracellular matrix proteins.
Secretory vesicles
The pinealocytes contain small intracellular vesicles that store and eventually secrete hormones like melatonin into the extracellular matrix and bloodstream.
Pineal Gland Blood and Nerve Supply
The pineal gland receives robust blood flow despite its protected location and lacks a blood-brain barrier. It has the highest blood flow rate by weight of any organ besides the kidneys.
The pineal receives arterial blood supply primarily from the posterior cerebral artery, a branch of the internal carotid artery. The glandular tissue drained by the pineal vein, a tributary of the internal cerebral vein.
The pineal gland also has substantial sympathetic innervation. Nerve fibers extend into the pineal parenchyma, where they interact with pinealocytes to influence melatonin synthesis. The nerves arise from the superior cervical ganglia.
Conclusion
While only the size of a pea, the pineal gland exhibits a surprisingly intricate interior and exterior anatomy. Its central location and separation from the rest of the brain contribute to its mysterious functions governing consciousness, dreams and our perception of reality. Continued study of pineal anatomy will uncover more secrets of this tiny gland.
Frequently Asked Questions
The pineal gland is centrally located in the middle of the brain behind the third ventricle. It sits between the two hemispheres and above the brain stem.
It is pine cone-shaped, which gives it its name. The gland is rounded or oval with a defined stalk and textured body resembling a miniature pine cone.
It contains pinealocytes, interstitial cells, glial cells, blood vessels, nerve fibers and extracellular matrix. Pinealocytes produce melatonin.
Despite its protected position, the pineal receives robust blood supply via the posterior cerebral artery, a branch of the internal carotid artery. It has extremely high blood flow.
The pineal stalk or peduncle connects the gland to its recess in the back of the third ventricle. Nerve fibers also directly link it to the brain for chemical signaling and regulation.
